The invention pertains to a chromium-containing cemented tungsten carbide body such as a cutting insert. While applicants contemplate other metalcutting applications, these cutting inserts are suitable for the machining (e.g., milling) of workpieces such as, for example, gray cast iron alloys.
Among the metalcutting processes, milling places the most demands on the cutting insert. The cutting insert repeatedly enters, cuts and then exits the workpiece, and thus sustains repeated mechanical and thermal shocks. Thermal shocks and mechanical shocks can each result in microchipping of the cutting edge of the cutting insert.
While earlier coated cutting insert have satisfactory performance, it would be desirable to provide a coated cutting insert that has improved ability to able to withstand the mechanical shocks and thermal shocks of a machining application such milling. Although these coated cutting inserts may have application to metalcutting applications in general, they would have specific application to the milling of gray cast iron alloys.
In one form, the invention is a coated cutting insert that comprises a tungsten carbide-based substrate that has a rake surface and a flank surface, the rake surface and the flank surface intersect to form a substrate cutting edge. The substrate comprises between about 5.7 weight percent and about 6.4 weight percent cobalt, between about 0.2 weight percent and about 0.8 weight percent chromium, tungsten and carbon. There is a coating on the substrate wherein the coating includes a layer of alumina applied by chemical vapor deposition (CVD). Preferably, the substrate comprises at least 70 weight percent, and more preferably, at least 90 weight percent tungsten and carbon.